1. Field of the Invention
The invention relates to control of enabling and disabling battery connections of a portable computing device.
2. Description of the Related Art
The advantages of portable computing devices continue to be recognized in an ever growing variety of personal and work activities. Being portable, these devices have many design features and constraints not present in their desktop counterparts. For example, such portable computing devices must rely on battery power rather than on the traditional source of power, the electrical outlet. This dependence on a battery source has introduced many new design constraints including: battery charge capacity, battery size requirements, battery under-voltage threats and battery operational impact. Given these constraints, designers have attempted to provide portable computing devices that best satisfy the consumer's needs while balancing the demands inherent in the above identified constraints.
The requirement that portable computing devices be able to function without the tether of a cord plugged into a standard electrical outlet requires that they operate on batteries. A unique feature of portable computing devices, not present in many other battery operated portable electrical devices, is a need for a continuous supply of power even after being turned off. This power demand is due to the operational nature of the volatile memory commonly contained in these devices. Volatile memory requires continuous power to retain the data stored therein. Because it is common for portable computing devices to contain volatile memory, it is important that such devices maintain a constant supply of power.
This need for a continuous supply of power presents many design challenges. For example, because batteries have a limited storage capacity, and because this capacity can be depleted through either operational use, or non-use (i.e., the volatile memory problem), such batteries need to be eventually recharged or replaced. In the case of replacement, when such batteries are replaced there is a period, between the removal of the old battery and insertion of the new battery, where no battery is connected to the device, and as such, there is a period where the volatile memory is without power. To prevent this period of non-power, one solution has been used which incorporates two batteries: a main or primary battery for supplying the normal operating power for the device, and a back-up or secondary battery for use as fail-over power. More specifically, during normal operations, whether turned on or not, the device draws its power from the main battery. It is only when the supply of power from this main battery is interrupted that the back-up battery is drawn upon. This dual battery design allows for the replacement of a main battery of a portable computing device without losing power and thus not losing the data stored in the volatile memory. Although this dual battery approach solves the problem of replacing replaceable batteries, it does not solve the problem discussed below relating to the general large size of replaceable batteries.
Further, there continues to be a demand for batteries that can supply continuous power for the longest amount of time before recharging. Generally, and especially among batteries of similar components, the larger the battery, the longer it can hold a charge. Thus, size not being a factor, very large batteries could be used to provide ever longer periods of charges. However, because it is almost always advantageous to produce portable computing devices that are as small as possible, and because the batteries used in such devices directly impact the ultimate size of such devices, the batteries need to be as small as possible, while providing as much power as possible. Further, user replaceable batteries must be designed with sufficient casing as to protect anyone handling such batteries from its contents. This encapsulation requirement means that such replaceable batteries are inherently larger than their non-replaceable counterparts. Thus, there is a tradeoff between using replaceable batteries with larger size and non-replaceable batteries that are smaller. Because of their smaller size, it is generally preferable to use non-replaceable batteries in portable computing devices.
Another design constraint inherent in using batteries is that batteries generally become damaged when their power is drawn below a particular level of charge (under-voltage). Therefore, to prevent permanent battery damage, it is important to prevent batteries from having their charge drawn down to such levels. It is not uncommon for circuitry to be included with portable computing devices which acts to disconnect or disable its battery when the battery charge level reaches a particular level. This is generally not an action one wishes to allow to occur on such devices since the disabling of the battery will cause the loss of data in the device's volatile memory.
It is also important to deliver the newly purchased portable computing device to the purchaser in the most user friendly condition as possible. Part of this user friendly condition relates to the batteries. For example, in the dual battery design discussed above, the most user friendly condition would be with both batteries installed and the system already powered up when the shipping box is opened. However, such a level of “user friendliness” is impractical and/or too costly as leaving the system fully powered up upon preparation for shipping would result in the batteries being fully discharged before reaching the purchaser. And further, without any type of automatic disabling circuitry, as discussed above, the batteries could suffer permanent damage. An alternative might be to ship the device with both batteries installed, but without leaving the system powered up. This approach would not result in the batteries being discharged as fast as the previous scenario, but would still likely result in the battery being fully discharged before reaching the purchaser. In practice, each of these two scenarios would result in very low user friendly conditions as both would require the purchaser to both diagnose the problem and replace or recharge the batteries before being able to operate the device.
A more user friendly condition would be to ship the device without any batteries installed. This would eliminate the need for the user to both diagnose why the device would not operate and to either recharge or replace the batteries. However, this would still require the purchaser to install the batteries before operating the device. Some manufacturers have devised a more user friendly way to ship their dual battery computing devices where the devices are shipped with the back-up battery already installed and requiring the purchaser to only install the main battery (both replaceable batteries). This is achieved by installing the back-up battery in the device where an insulator is placed between this battery and its electrical contact and where the purchaser is required to pull the tab connected to the insulator to remove the insulator and to allow for the electrical connection between the back-up battery and the device contacts. Although this removes the need to install two batteries, it still requires two actions by the purchaser before the device is ready for use. The possibility also exists that the tab might separate from the insulator leaving all or part of the insulator between the back-up battery and the electrical contact. Further, as discussed above, this design is less advantageous than other designs using non-replaceable batteries since the device would be required to be larger to accommodate the larger replaceable batteries.
Another approach to the shipment of the portable computing devices has been to ship the devices with the battery(s) installed, where such devices have circuitry including a battery disabled and battery enabled modes, and the device is shipped with the device in the battery disabled mode. For example, such designs as the Compaq iPAQ 3700 series have included the use of a single non-replaceable battery with such disabled and enabled modes. As shown in FIG. 3, such a unit 500 is shipped in the disabled mode and the purchaser activates the unit, i.e., the user changes the unit from the battery disabled mode to the battery enabled mode, by locating a sliding door 522 on the bottom side 530 of the unit 500, and using the accompanying stylus (not shown), sliding the door 522 open, and flipping a slide switch 520 to the on position. Note that reset button 514 is not used in this battery enable procedure. This approach has its drawbacks as users might be confused as to how to power up the system. The users might have a problem identifying the door, or that the switch was behind that door. Another potential negative aspect of this approach is that the door may potentially develop a rattle over time.
Regardless of which of the above approaches involving shipping the batteries in a disabled state is used to ship the portable computing device, each has the common feature of an activation scenario that cannot easily occur accidentally during shipping. As explained above, one needs the batteries to be installed, while another needs a plastic tab removed, and finally another needs a switch behind a door to be thrown.
Designers have also chosen to include a disable battery function in their portable computing devices. Designers have provided different ways, either passive or active, for users to place the units in a disabled state. The passive designs, where a physical break between the battery and the device is required, include those devices where removable batteries are used and the only way to accomplish a disabled state is to remove the batteries. For example, the Compaq Aero 1550 Pocket PC required the removal of both a main battery and a back-up battery. Active designs, where some form of button pressing or switching throwing is needed, include devices such as the Compaq iPAQ 3700 series which simply required the opening of the door at the bottom of the unit and throwing the switch to the disabled position. Another unit was the Hewlett Packard Jornada that required that the unit be turned off using the power button, followed by the simultaneous pressing of the reset button and the power button. The Casio E-115 required the simultaneous pressing of the power button and reset button for two seconds which invokes a screen prompt, followed by the pressing of a control button.